Recent advances in the hearing sciences have been based on a new class of auditory response termed otacoustic emissions that can be objectively measured in the ear canal of all normally hearing persons. Based on this knowledge, it is now possible to propose to develop objective hearing- screening instruments for the assessment of auditory dysfunction based upon the absence of emitted responses. One class of emission elicited by continuous pure tones is called the distortion-product otacoustic emission (DPOAE). In comparison to the other types of emissions, DPOAEs offer a significant advantage in that they can provide a detailed objective "audiogram" within a reasonably short time period. Moreover, DPOAEs can be measured over a relatively large range of hearing loss. During Phase I of this project, we accomplished the goal of compressing existing laboratory instrumentation for collecting DPOAEs into microcomputer-controlled devices based upon two popular personal-computer systems, the Apple Macintosh and the IBM/PC. Both systems utilized a single digital-signal processing board to replace the existing laboratory equipment used to generate and analyze DPOAEs. Preliminary results indicate that the Macintosh microcomputer system can be finalized in Phase II into a portable, easy-to-operate instrument that will allow collection of sufficient normative data in applied settings so that the device can be rapidly refined into a commercial package capable of performing routine hearing screening in newborns, infants, children, and adults. The specific aims of the Phase-II project focus on completing the development of the Macintosh version of the system including the design and testing of microphone probes that can be used in children and adults, the determination of probe-calibration procedures, the development of final software/user interfaces, the design and testing of software-based noise-rejection strategies, and the preliminary evaluation of the system in clinical and industrial populations. A final goal will be to continue the development of an IBM/PC version of the device that will be compatible with the numerous personal computers already located in many research and clinical facilities.